A man accused of intentionally killing his 22-month-old son by leaving him in a hot car had read articles about living a child-free life and was "sexting" with six women while his son died, police in the southern United States told a court hearing in which a judge ordered the case to trial.

Justin Ross Harris, 33, also had two life insurance policies on his son, Cooper, and had twice watched a video about overheating deaths in cars before his son died, according to police testimony given on Thursday in the court in Atlanta, Georgia.

Judge Frank Cox found that prosecutors had presented enough evidence to try Harris for murder and child cruelty.

Harris' lawyer argued that his client had been distracted, and that prosecutors had only brought up the sexting to "publicly shame" Harris, who is married. Two of Harris' friends and his brother testified he seemed to be a loving father.

"We plan to show he wanted to lead a child-free life," assistant district attorney Chuck Boring told the court.

"He's got this whole second life he's living with alternate personalities and alternate personas" with his sexual activities online.

Officials said Harris had also watched videos on Reddit of people getting killed, had searched for Georgia laws on the age of consent and had searched for "how to survive prison".

Harris left his son, Cooper, in an SUV in a car park at his work place at a Home Depot in an Atlanta suburb at 9.25am on a day when the temperature rose above 30 degrees Celsius, police said.

Harris left work at 4.15pm and stopped his car suddenly near a shopping centre where he pulled his son's body out of the car, apparently in distress after discovering what he had done.

"He seemed upset, his behavior was considered erratic, he would be yelling and screaming 'what have I done, my child is dead', then he would stop with a blank look on his face," Stoddard testified, summing up witness' accounts.

But during Thursday's court hearing, police said that was not the first time Harris had gone back to his car since he arrived at work.

Police said surveillance video showed that after having lunch, Harris went to put light bulbs inside the car, where his son was strapped into a rear-facing car seat. As Harris walked away from the car, he hesitated as another man walked by the car, police said.

Officials also raised questions about how Harris could have driven 3km before noticing his son's body in the car.

This article appeared in the South China Morning Post print edition as Dad faces trial over son's death in hot car

Wow. I'm 100% against capital punishment, but I would love to lock this man in a car for 8 hours on a hot day.I hope any unhappy fathers who contemplate such depravity see this horrible story and opt to do what any respectable coward does and just run-out on their family.This guy disgusts me.